I'd go back to January of 1982 and start telling everybody about the future. I'd start with things in the near future just to get people's attention. I'd talk about how The Wrath of Khan was going to be considered the best Star Trek movie for decades to come, and how influential E.T. was going to be. I'd talk about how the soundtrack to Conan the Barbarian would be widely considered to be the best soundtrack for decades to come.
I'd talk about the future of the Hubble space telescope, how the Supercollider in Texas was never going to work out, how CERN produced the Higgs Boson, how they discovered the expansion of the universe is accelerating, and I'd tell them about the internet and all kinds of other things. I'd tell them who the next few Presidents were going to be, about the the Challenger explosion, and about the collapse of the Soviet Union and the fall of the Berlin Wall.
I don't know I get a kick out of imagining that scenario, but I do.